For example, in a process of hot-stretching steel wires by heating at a high temperature, a mill scale (black film) or a scale (oxide film) including the mill scale is generated on the surfaces. In order to remove these scales, a method now is employed according to which the scales are trimmed off by using a ring-shaped peeling blade before entering a wire-stretching die.
At present, further, a method of treatment with acid is frequently used in which metal wires in a pool of acid is dipped to dissolve and remove the scales.    Patent document 1: JP-A-2001-32042